This invention relates generally to heliothermal systems, and in particular to a solar-energy air-heating system which makes use of collector modules that are readily attachable to the exterior wall of a building to create a solar collector unit which forms an air flow loop with the building interior whereby air drawn from the interior is heated in the course of its passage through the unit before being returned to the interior.
With the growing scarcity of fossil fuels and their sharply rising cost, a pressing need exists for an inexpensive and abundant energy source. The inexhaustible nature of solar energy and its significant magnitude over relatively small collection areas is such as to encourage its exploitation, even at low efficiencies of recovery. Despite variations encountered in solar radiation in the course of a day, this energy can be used in a heliothermal process in which the incident radiation is absorbed and converted into heat for heating air or water to moderate temperature levels.
In considering a heliothermal system, one must draw a distinction between economic and operating efficiency. The operating efficiency of any thermal energy conversion system, including a solar energy collector, is determined by the ratio of heat obtainable to useful heat received. But economic efficiency is measured by heat units obtainable in a unit time per dollar invested. Because low-level, free energy is available in great abundance within a relatively small area, one may tolerate a low operating efficiency if the system is inexpensive. The desideratum, therefore, is a system of the lowest possible cost and of the highest possible efficiency. In evaluating the comparative efficiency of solar energy systems, the most practical system is the one that generates the greatest useful energy output per dollar invested.
Typically, a solar-energy water-heating system includes a collector having water-filled tubes fastened to a heat-conductive plate, usually of blackened copper, as well as piping to connect the collector to a storage tank and a pump to circulate the water. The construction and installation costs of a solar-energy water-heating system are substantial, to say nothing of maintenance and other problems associated with such systems, such as water freezing in the pipes or leakage therefrom.
As pointed out in the May 1982 issue of Consumer Reports in an article entitled "Solar Water Heaters," though heaters of this type save energy, they do not actually save money; for the equipment and installation costs, unless heavily subsidized, are still too high to make a return in the form of energy savings, attractive.
An alternative approach to solar heating obviating the need for circulating water is to provide a solar-heat collecting panel in which heat absorbed by the collector surface exposed to solar radiation is transferred to air passing across the surface, the heated air being then used to heat the interior of a building provided with a conventional forced air heating system. Among patents which disclose solar heated air systems are patents to Parker, U.S. Pat. No. 3,919,998; Pulver, U.S. Pat. No. 3,994,276; and Keyes et al., U.S. Pat. Nos. 3,946,730 and 3,946,721.
An important advantage of a solar heated-air system over a solar water system is the absence of pipes in the collector and in the water lines connected thereto. This makes possible a significant reduction in construction, installation and maintenance costs. However, as will be evident from the above-identified patents, with existing solar air-heating collectors, it is still necessary to construct the collector so that its dimensions are appropriate to the siding or roof of the building on which it is to be installed. This means that the collectors have to be custom designed at the factory for a particular building or constructed at the building site, either procedure being relatively costly and requiring skilled craftsmen. In the case of the Keyes et al. arrangement, the solar collector is not installed on the building but occupies a separate cabin distinct from the building, a still more expensive arrangement.
Because of high labor costs and the scarcity of skilled craftsmen in the United States, many householders have become do-it-yourselfers. And for that reason, hardware stores and other establishments catering to home owners carry various products in knock-down form adapted to be assembled and installed by the householder using screw drivers and other simple tools. But the inherent nature of solar energy systems of the hot air or water type has heretofore been such that the system does not lend itself to packaging and transportation in knock-down form, or for installation by a do-it-yourselver having minimal skills.